Vulnerability · Published Oct 1, 2026 · Assigned by GitHub_M
CVE-2026-104183stream-json: Prototype pollution: Assembler writes this.current[this.key] on plain objects
Medium 5.1
In plain English
A medium-severity prototype pollution in stream-json from uhop. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
stream-json is a micro-library of stream components for processing JSON and JSONC with a minimal memory footprint. Prior to 3.6.0, Assembler materializes object properties with plain assignment, so an input key named __proto__ invokes the inherited setter and causes parsed object prototype replacement instead of creating an own data property. Applications that make authorization or feature decisions from inherited values can therefore consume attacker-controlled properties, and a null prototype can disrupt code that expects Object.prototype methods. The researcher treats parsing untrusted JSON as part of the project contract, while the maintainer states that documented inputs are locally owned dumps, exports, or logs and characterizes the attack vector as local. The global Object.prototype is not polluted. This issue is fixed in version 3.6.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | stream-json | 3.6.0 | GHSA-mjw6-4jj6-33hc |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| uhop | stream-json | < 3.6.0 |
Weakness: CWE-1321 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
References
- https://github.com/uhop/stream-json/security/advisories/GHSA-mjw6-4jj6-33hc x_refsource_CONFIRM
- https://github.com/uhop/stream-json/commit/2f2d35bbb547306991ded6487a279154d865a358 x_refsource_MISC
- https://github.com/uhop/stream-json/releases/tag/3.6.0 x_refsource_MISC